Ceramic sealed window



Oct. 5, 1965 HlsAsHl TAGANO 3,210,699

CERAMIC SEALED WINDOW Oct- 5, 1955 HlsAsHl TAGANO 3,210,699

CERAMIC SEALED WINDOW Filed Dec. 19, 1962 2 Sheets-Sheet 2 BY 057-@ az eme, 5955A $5195 'JbFFf/f United States atent 3,210,699 CERAMIC SEALED WINDW Hisashi Tagano, Shiba Mita, Minatoku, Tokyo, Japan, assignor to Nippon Electric Company Limited, Shiba Mita, Tokyo, Japan Filed Dec. 19, 1962, Ser. No. 245,722 Claims priority, application Japan, Dec. 21, 1961,

.S6/46,871 6 Claims. (Cl. S33-98) This invention relates to electromagnetic-wave transmission apparatus and more particularly to an hermetical- 1y sealed window for electromagnetic-wave transmission devices wherein a ceramic plate is mounted within such window or space provided in a metallic member or microwave or millimeter-wave circuit, such as, for example, a waveguide portion, waveguide coupler or cavity resonator which may be employed in electromagnetic- Wave transmission devices, such as, for example, millimeter-wave electron tubes.

Present day mircowave circuits have need in many applications thereof for the use of a ceramic window within the waveguide structure. Such structures have conventionally employed a dielectric material for transmitting the electromagnetic-wave. Some of the dielectrical materials which have been employed are mica, glass, ceramics, etc. Such windows are integrated into the microwave structure by virtue of an hermetic sealing operation. As one exampie, such a window formed from a mica plate is sealed in an oxidizing or a neutral atmosphere to the metal portion of the waveguide structure by a soldering operation where a soldering glass having characteristic of a low melting point such that the mica plate will not be dehydrated so as to remove the water of crystallization contained therein. The mica plate is sealed to a metal portion having a coeiiicient of thermal expansion substantially equal to the thermal expansion of the mica plate. As another example, a plate formed of glass may be employed in the waveguide structure by melting the peripheral portions of the glass plate in the medium of an oxide lm of the metal so as to adequately secure the glass plate to the waveguide structure. As a further example, a window formed from a ceramic plate may be joined to the waveguide structure by first providing a metallized surface upon the peripheral surface of the ceramic plate and subsequently soldering said metallized surface to the metal portion of the waveguide structure using a solder having a high melting point and performing the soldering operation in either a reducing atmosphere or in a vacuum.

An analysis of the aforementioned operations shows that the ceramic sealed window is mechanically stronger and both thermally and electrically superior to windows employing mica or glass plates and has the further advantages of providing a purer or non-contaminated completed structure due to the fact that the sealing operation is performed in a manner such that the metallic parts of the assembly are not subjected to any oxidation.

Ceramic plate windows, however, have a disadvantage in that the coetiicient of thermal expansion of such ceramic plates does not coincide well with the thermal expansion of the metallic members to which it is affixed. Glass plates therefore, are superior to ceramic plates for the reason that their coeiiicients of thermal expansion are more nearly equal to the metallic surfaces to which they are affixed.

The large differences of thermal expansion which exist between ceramic plates and their cooperating metallic surfaces introduce significant problems into the manufacture of ceramic sealed windows. Some of these are the creation of excessive seal stresses and the difficulties encountered in the soldering operation. One method of f'ie overcoming such sealing stresses consists of the employ ment of alumina ceramic plates and metallic waveguide members composed of an iron-nickel-cobalt alloy which elements have superior thermal expansion characteristics. One alloy which has been employed is Kovar, which name is the registered trademark of the Carborundurn Company, It has been found, however, that even the above -ceramics and alloys have been insuiiicient to alleviate the above disadvantages.

Another procedure in overcoming the above mentioned problems is to provide a sealed window construction such that the differential in thermal expansion between `the ceramic and the metal will not be the material factor determining the strength of said Seal. Such an objective is obtained by making the metallic body as vthin as `possible and providing a ceramic plate of substantial thickness so that the stress produced in the sealed portion of the ceramic body is small. However, it has been found that ceramic plates of substantial thickness severely attenuate the electromagnetiowaves passing therethrough thereby prohibiting their use.

A second problem which presents itself due to the use of the above mentioned alternative structure is that the shape and dimensions of protrusions and depressions (i.e., convex and concave surfaces), which are present in such structures either along the inner surface of the waveguide structure or along the surface adjacent the ceramic sealed window seriously effect the electromagnetic-waves passing therethrough. Also, the ceramic sealed windows may further effect the transmitted electromagnetic-waves due to the material shape or dimensions of the ceramic plate.

The device of the instant invention provides a method for forming such a ceramic sealed window which cornpletely overcomes the problems introduced by thermal stresses, while at the same time providing a ceramic sealed window structure which has transmission characteristics superior to such characteristics of prior art devices.

The instant invention is comprised kof a method for forming a ceramic sealed window structure which method is comprised of providing a ceramic plate for use as said window, which plate is formed so as to have dimensions suitable for use in the waveguide structure. A ceramic frame is then provided, which frame is formed so as to position and support the ceramic window along its interior surface. The ceramic frame is suitably coated with a metallic surface employed for the purpose of suitably securing the frame to metallic supports provided in the waveguide structure. A suitable metallic coating is likewise provided along the peripheral surface of the `ceramic plate window and the cooperating metallic surfaces of the ceramic plate and ceramic frame are then suitably soldered or joined to one another. The thickness of the ceramic plate window is selected so as to have minimum attenuation characteristics. The ceramic frame, however, may be substantially thicker than the ceramic plate window so that thermal stresses between the waveguide rnetallic supports and the ceramic frame are not consequential. Since the thermal expansion characteristics of the ceramic frame and the ceramic plate are substantially identical no thermal stresses exist therebetween. In addition to the above, the use of the ceramic plate and cooperating ceramic frame provides a structure which presents neither protruding nor depressed surfaces to the electromagnetic-waves transmitted therethrough so that the quality of the electromagnetic-wave is not hampered by the ceramic sealed window structure. The wave is not severely attenuated and all thermal stress problems have been completely overcome.

It is therefore one object of the instant `invention to provide a ceramic sealed Window structure which is designed to completely overcome the problem of thermal stress between the sealed window and the cooperating waveguide structure.

Another object of the instant invention is to provide a ceramic sealed window structure which completely overcomes the disparity in thermal expansion between the ceramic window plate and the cooperating metallic waveguide structure.

Another object of the instant invention is to provide a ceramic sealed window structure which provides a regular interior surface to the electromagnetic-waves transmitted therethrough so as to have no eifect on the quality of such waves.

Another object of the instant invention is to provide a method for forming a ceramic sealed window structure which overcomes the problem of thermal stress between the sealed window and the cooperating waveguide structure.

Another object of the instant invention is to provide another method for forming a ceramic plate structure which overcomes the disparity in thermal expansion between the ceramic window plate and the cooperating metallic waveguide structure.

Still another object of the instant invention is to provide a method for forming a ceramic plate window structure having a regular interior surface to the electromagnetic-waves transmitted therethrough so as to have no effect on the quality of such waves.

Another object of the instant invention is to provide a sealed ceramic plate window structure Which employs a novel ceramic frame for mounting the ceramic plate window to the metallic waveguide structure.

Still another object of the instant invention is to provide a sealed ceramic plate window structure wherein the ceramic plate window and the ceramic frame are suitably coated with metallic surfaces for securing said elements to the metallic waveguide structure.

These and other objects of the invention will become apparent when reading the accompanying description and drawings in which:

FIGURES l and 2 are cross sectional views of prior art waveguide structures showing the window portion thereof comprising a metal space which operates as a microwave or millimeter-wave circuit employing a ceramic sealed Window for transmission of the electromagnetic-wave.

FIGURES 3, 4 and 5 are similar cross sectional views of such electromagnetic-wave devices employing a ceramic sealed window designed in accordance with the principles of the instant invention.

Referring now to the drawings; FIGURE 1 shows a conventional waveguide structure 100 having a relatively small ceramic sealed window structure 101 comprising a ceramic window plate 102 which is substantially thin enough to effect better penetration therethrough of the electromagnetic-wave. While the view shown in FIG- URE 1 does not show the peripheral dimensions of the ceramic plate window 102, it should be understood that plate 102 may be of any configuration generally employed in such waveguide structures, such as, for example, square, rectangular, circular, etc. A metallized layer 104 is provided along the inner surface of ceramic plate window 102 adjacent the periphery thereof. This metallized layer is suitably soldered to a thin, flexible frame-shaped metal plate 105 having substantially the same conguration as the periphery of ceramic window plate 102. The soldering joint is formed at position 103.

Window frame 105 is designed to be relatively thin in order that the ceramic window plate 102 will not be damaged by the stress caused along the sealing junction 103 due to the difference in thermal expansion characteristics of the ceramic and the metal. The metal frame 105 is in turn soldered at junctions 106 to a metallic waveguide coupler 107. The waveguide coupler 107 is suitably connected such as by soldering to metallic waveguide portion 108 at the juncture or seam 109. Coupler 107 is provided with suitable apertures 112 for connecting a like coupler or other waveguide structures thereto through the use of suitable fastening means (not shown). The ceramic sealed window structure 101 of FIGURE 1 has the disadvantges in that with the use of a Very thin ceramic window plate 102 the metallic frame 103 is provided with depressions and protrusions 110 and 111 respectively, which are provided for the purpose of yielding to overcome the aforementioned thermal stresses. These uneven metallic surfaces alter the quality of the electromagnetic-wave transmitted therethrough, such as to change their phase, frequency, mode, etc. In addition to the above disadvantages, the window structure 101 is extremely weak and may be subjected to damage due to atmospheric pressure or other external forces. This weakness is caused by the fact that in order to provide such a disc-seal the metallic frame 105 must be extremely thin in order to avoid breakage of the ceramic window plate 102.

FIGURE 2 shows another conventional waveguide structure 200 employing a ceramic window structure 201. Structure 201 is comprised of a ceramic window plate 202 having a metallized layer 203 along its peripheral surface. Ceramic window plate 202 is soldered at the juncture 204I to waveguide 205 only a segment of which has been shown for purposes of clarity. The waveguide 205 is in turn soldered at a junction 200 so as to join a waveguide coupler 207 thereto. Coupler 207 is provided with apertures 208 identical in function to the apertures 112 of FIGURE 1. The arrangement of FIGURE 2 is termed a compression seal and is employed due to the fact that a ceramic exhibits characteristics which are superior under compression than they are under tension. This permits the metal of the waveguide portion 205 to be so selected as to have a greater coefficient of thermal expansion than the ceramic material of the window plate 202. The problems encountered in such structures are caused due to the fact that the window plate 202 is substantially large or the shape thereof is not circular in the case where a circular waveguide is used or is not perfectly square or rectangular in the case where square or rectangular waveguide sections are used. To be more specific, the use of a ceramic sealed window having a substantially large diameter is required in electron tube structures which operate at substantially long-wave electromagnetic-waves. Ceramic plates of such large diameters are required in order to properly mate with the waveguide sections into which they are inserted. In such large diameter or large dimension structures the coefficients of thermal expansion becomes significant since during operation thereof an extremely large gap may be formed between these elements during the soldering operation which is performed in a high temperature region. If such large gaps are developed it has been found that the solder will fail to completely ll such gaps without leaving some void spaces therebetween. For example, it has been very diicult to solder a alumina Ceramic of a 100 millimeter diameter to a waveguide portion 205 formed of a Kovar type alloy such that the solder employed will completely ll up in a uniform manner the gap formed between the ceramic window plate 202 and the waveguide section 205. The gaps in such structures have been found to be within the range of 0.30 to 0.50 millimeter.

The soldering operation becomes even more difficult in cases where the window plate 202 is not circular but has an elliptical or rectangular conguration because the differences in the widths of the gap in the direction of the major and the minor diameters or of the longer and the shorter widths.

Another trouble encountered in such window structures is that the window plate 202 has been found to warp and crack at the surface region due to the fact that the surface region undergoes excessive stress which is caused by the resultant force of the compression exerted in a direction parallel to the surface of window plate 202. Also atmospheric pressure or other external forces which are exerted substantially perpendicular to the window plate 202 will cause such warping and cracking in cases where the ceramic window plate 202 is made substantially thin in order to minimize attenuation of electromagnetic-waves during the transmission of such waves through the ceramic plate Window 202.

By employment of the instant invention it is possible to completely alleviate the above mentioned qualitative and constructional diculties found in the conventional ceramic sealed window structures while at the same time providing a ceramic sealed window of excellent quality. These characteristics can best be seen by a consideration of the structure of the instant invention, one embodiment of which is shown in FIGURE 3 which portrays a wave guide structure 300 employing a novel ceramic seal window structure 301. The window structure 301 is comprised of a ceramic frame 302 which is formed from the Same Ceramic material or a similar ceramic material having like thermal expansion characteristics as the ceramic Window plate 303 provided in the window structure 301. This arrangement provides a suiciently strong construction for such sealing and is designed in such a way as to be regarded electrically as a metallic frame, for purposes to be more fully described.

The window plate 303 of waveguide structure 300, which is adapted for use as the output portion of a relatively small electron tube, for example, is provided with a shoulder, or a notch, 305 along the entire periphery thereof so as to form a step-like profile. A suitable metallized surface 304 is provided along the surface of notch 305 for purposes of effecting a suitable seal in a manner to be more fully described The ceramic frame 302 is designed to have an interior conguration substantially identical to the peripheral configuration of window plate 303 so that if plate 303 has a circular configuration the interior surface of ceramic frame 302 is likewise circular. All exposed surfaces of ceramic frame 302 are coated with a metallized surface 306, which surface is of the same material as the metallized surface 304. The window plate 303 is soldered to the frame 302 along the metallized layer 304. The adjacent surface of frame 302 is notched at 307 in order to better position and support window plate 303.

Frame 302 is then soldered along its vertical lefthand surface to the flanged portion 309 of waveguide section 308 so as to form the soldered seam 310. The right-hand vertically aligned surface of ceramic frame 302 is suitably soldered to metallic cover plate 311 forming the soldered seam 312 therebetween. Since ceramic frame 302 has a thickness which is more than sullicient to withstand the difference in thermal expansions between ceramic member 302 and metallic flanges 309 no thermal stresses appear in the window plate 303 as it is sealed to the frame 302 which is formed of the same or similar ceramic material. It is therefore possible with this arrangement to select the thickness of window plate 303 to be as small as possible so long as it withstands the atmospheric pressure while at the same time minimizing the loss or attenuation of the electromagnetic-wave passing therethrough.

Each of the metallized layers 304 and 30d are formed of an electrically low loss material and may be formed on window plate 303 and ceramic frame 302 by sintering at a high temperature and in a reducing or neutral atmosphere, a coated layer which contains in the most part molybdenum, molybdenum and manganese, tungsten, or other metallic powder, and then electroplating, brazing, or otherwise in covering the sintered layer with another metallic layer consisting of one or any combination of nickel, copper, gold, silver, or the like.

As can be seen from the waveguide apparatus 300, shown in FIGURE 3, the interior, surfaces thereof are extremely uniform and regular such that neither depressions nor protrusions (i.e. convex or concave surfaces) appear anywhere within the interior area 300 of the waveguide structure 300.

An alternative arrangement for sealing window plate 303 to ceramic frame 302 may be employed which comprises the steps of providing ceramic frame 302 with a metallized surface layer 306 and sealing ceramic 4window plate 303 without the metallized layer 304 thereto by means of a high softening-point glass, such as an aluminosilicate glass, in a mixed atmosphere of nitrogen and hydrogen wherein it has been found that the aforementioned glass provides a very effective seal.

FIGURE 4 shows an alternative waveguide structure embodiment 400 which may be employed in applications where relatively large-sized ceramic sealed windows are required. The window plate structure 401 thereof is comprised of a ceramic window plate 402 having a metallized surface 403 which is sealed by a suitable soldering material 404 to the metallic surface 406 provided on ceramic frame 405. The ceramic frame 405, metallic surface 406, solder junction 404, metallized surface 403 and ceramic window plate 402 are substantially identical in both structure and function to the like elements of FIG- URE 3. As mentioned previously, ceramic window plate 402 may be sealed to ceramic frame 405 by the alternative method of employing a high-softening point glass in place of the soldering material 404 and without the metallized layer 403.

Ceramic frame 405 is soldered along seams 407 and 407 to metal supporting members 408 and 408 respectively, which members are made thin with a view to reducing the sealing stress to a minimum. For convenience, the assembly of elements 402, 405, 408 and 40S', etc. will hereandafter be identified by the name window assembly. The window assembly is sealed along seams 409 and 410 to a metallic reinforcing member or frame 411 having an accompanying waveguide section 412 and waveguide coupler 413 associated therewith. Waveguide section 412 is sealed to member or frame 411 by means of solder seam 409 while waveguide coupler 413 is fastened to member 411 by bolts 414. Suitable apertures 41S are provided in coupler 413 for connecting the waveguide structure 400 to associated apertures.

The window assembly or structure 401 of FIGURE 4 has the distinct advantage of avoiding thermal stresses due to the fact that the `ceramic frame 405 and ceramic window plate 402 are made of the same or similar ceramic material and that the mechanically strong frame 405 is disc-sealed to the thin metallic supporting members 40S and 408 such that no sealing stresses are transmitted to the ceramic window plate 402. In addition to the above, in applications which require the usage of substantially large diameter window plates the structure of FIG- URE 4 has no diiculties described in conjunction with the conventional ceramic sealed windows shown in FIG- URE 2 due to the fact that large gaps may form between the waveguide section 205 and the ceramic plate window 202. This is so because even though the soldering be performed at extremely high temperatures both the ceramic window 402 and the ceramic frame 405 will be formed to the same degree. Compression stresses are avoided by the usage of substantially thin supporting members 408 and 400 which are secured to a relatively thick and hence mechanically strong ceramic frame 40S. The employment of supporting member or frame 411 and coupler 413 further protect the ceramic window assembly 401 against external forces which may be applied thereto upon attaching or detaching the waveguide structure 400. The supporting members 408 and 408 to which the ceramic frame 405 is disc-sealed may be made of any metal of any thermal expansion characteristic, the only requirement being that the supporting members be substantially thin. While FIGURE 4 shows a substantially flat or planar ceramic window plate 402 a none planar window plate, such as, for example, a spherical or conical window plate may be employed in applications where the sealing must be effective against atmospheric pressure or compressed gases purposely introduced into the waveguide structure in large power transmission applications.

FIGURE shows still another embodiment of the invention wherein a waveguide assembly 500 is provided with a window assembly 501. Like elements of the waveguide structure 500 bear numeral designations identical to the numeral designations of FIGURE 4 with the exception that the rst digit has been changed from the number 4 to the number 5, for example, whereas the ceramic window plate of FIGURE 4 is designated by the number 402, the ceramic window plate of FIGURE 5 is designated by the number 502. The embodiment of FIGURE 5, however, shows the ceramic plate window 502 aligned at an angle less than a perpendicular angle to the sides of waveguide sections 512 and 512'. Briefly, the window plate 502 is provided with a metallized surface, as shown at 503 along its peripheral edge, while ceramic frame 505 which is formed of the same material as ceramic window plate 502 is metallized along its surface providing thereby the coating 506. The frame 505 and plate 502 are sealed with solder along a seam 504. The ceramic frame 505 is soldered to supporting members SGS and SGS along seams 507 and 507. Support members 508 and 508 are suitably soldered to waveguide sections SI2 and 512 respectively, and to supporting or reinforcing frames Sil and 513 respectively, along seams 599 and Slt?, respectively, joining these supporting members to the reinforcing frames 511 and 513 respectively, reinforcing frames 511 and 513 being fastened to one another by fastening means 514. The reinforcing means or frames 511 and 513 are likewise sealed to waveguide sections SI2 and 512' respectively, along seams 509 and 510. Even in the assembly 500 of FIGURE .5 wherein the ceramic window plate 502 forms an acute angle with the waveguide section sections 512 and 512 it can be seen that it is still possible to provide a relatively simple construction while at the same time retaining superior mechanical characteristics, whereas in prior art devices this is not the case since such structures will present undesirable depressions and/ or protrusions of the type described with reference to the description of FIGURE 1 due to the fact that the considerations of angular orientation of the ceramic plate window 502 must be taken into account in addition to the problems encountered due to the use of the metallic frame 105 used in the arrangement of FIGURE l which metallic frame was so designed as to minimize the thermal expansion differences between metal and ceramic.

As has ybeen explained, it is possible with the invention to freely design a ceramic sealed window and to easily manufacture the same having such a construction wherein electrical performance .and thermal and mechanical strength are sufficiently taken into consideration, with the result that the invention is applic-able not only to the embodiments described above but also to a hermetic ceramic end seal of a waveguide iilled with special gas for the sake of transmission of .a millimeter wave, a hermetic ceramic seal within a cavity resonator, a hermetic seal ceramic coupling window for other space circuit, and so forth.

Although there has been described .a preferred embodiment of this novel invention, many variations and modilcations will now be apparent to those skilled in the art. Therefore, this invention is to be limited, not by the specific disclosure herein, ybut only by the appending claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are dened as follows:

1. A hermetically sealed ceramic window assembly for use in waveguide structures comprising ya ceramic window plat-e; a ceramic window frame; a pair of metallic support members; a pair of reinforcing frames; said wind-ow frame having `a central opening for positioning and securing said ceramic window plate; said window frame having a metallized surface coating over its entire surface Adapted to `facilitate sealing of the window frame to the ceramic window plate and said pair of metallic support members, said ceramic window plate having a metallized surface coating only along its peripheral edge to facilitate sealing of .the window plate to the ceramic window frame, said ceramic window plate being separated from said waveguide assembly by :said window fra-me, each of said support members having a rst arm sealed to said ceramic window frame and a second arm sealed to said reinforcing frame and the wave-guide structure; first means for sealing said ceramic window plate to said ceramic window frame; second means for sealing said first arm to said -ceramic window frame; third means for sealing said lsecond arm to said reinforcing frame and said waveguide assembly; .and fourth means for sealing said reinforcing frame to said waveguide assembly; said first through fourth means for :sealing being solder; the thickness of said support member being controlled to substantially eliminate thermal stress from said ceramic window plate; said reinforcing frame fastening said ceramic window frame through said support member to protect said ceramic window plate and said ceramic window Iframe from external forces.

2, A hermetically sealed ceramic window assembly for use in waveguide structures comprising a ceram-ic window plate, a ceramic window frame, the thickness of said window frame being substantially greater than the thickness of said window plate, a metallic waveguide section, said ceram-ic window frame provided with a central opening for positioning and securing said ceramic window plate within said opening, said window frame being covered with a metallized surface coating over its entire surface to facilitate sealing of said ceramic window frame to said ceramic window plate and said metallic waveguide section as well as providing electrical substantially uniform surface conductivity `for the entire surface of said ceramic window frame, said ceramic window plate being covered with `a metallized surface coating only along the peripheral edge thereof to facilitate sealing of said window plate at the inside of said central opening to said window frame, said ceramic window plate being separated from said waveguide section by said window frame.

3. The ceramic window assembly of claim 2. further comprising solder means for sealing said ceramic window plate to said ceramic window frame and said ceramic `window frame to said metallic waveguide section by solder.

d. A hermetically sealed ceramic window assembly for use in waveguide structures comprising a ceramic window plate, a ceramic window frame, the thickness of said window frame being substantially greater than the thickness of said window plate, a metallic supportin-g member, and a waveguide section, said ceramic window frame being provided with a central opening for positioning and .securing lsaid ceramic window plate within said opening, said ceramic window frame being covered with a metallized surface coating over the entire surface thereof to facilitate sealing of said ceramic window frame to said ceramic window plate and said metallic supporting member and as well as providing electrical Vsurface conductivity for the entire surface of said ceramic window frame, said cera-mic window plate being covered with a metallized 'surface coating only along the peripheral edge thereof to facilitate sealing of said ceramic window plate to said ceramic window frame, said ceramic window plate being separated from said metallic supporting member 4by said window frame, one end of said metallic supporting member vbeing sealed to said ceramic window frame and the other end being sealed to said waveguide section, solder means for sealing said window plate and said .support member to said window frame.

5. A hermetically sealed ceramic window assembly for use in waveguide structures comprising a ceramic window plate, a ceramic window frame, the thickness of said Window frame being substantially greater than the thickness of said window plate, a metallic supporting member, and a waveguide section, said ceramic window iframe being provided with a central opening for positioning and securing said ceramic Window plate within said opening, said ceramic Window frame being covered with a metallized surface coating over the entire surface thereof to facilitate sealing of said ceramic window frame to Iboth of said ceramic window plat-e and said metallic supporting member as well as providing an electrical surface conductivity for the entire surface of said ceramic window frame, said ceramic window plate being covered with 'a metallized .surface coating only along the peripheral edge thereof to yfacilitate sealing of said ceramic window plate to said cer-amic Window frame, said ceramic window plate being separated from said metallic supporting member by said ceramic window frame, one end of said metallic supporting .member being sealed to said ceramic window frame and the other end lsealed to said wavegu-ide section, said metallic supporting member having a smooth surface devoid of any depressions or protrusions to maintain the quality of the electromagnetic wave transmitted through said cer-amic window assembly, the thickness of said metallic supporting member having been controlled so as to substantially eliminate a .sealing stress in said ceramic window frame, and solder means for sealing said window plate and said support member to said window frame.

`6. A ceramic window assembly for use in waveguide structures comprising a ceramic window plate, a ceramic window frame, the thickness of said Window frame being substantially greater than the thickness of said window plate, a metallic waveguide section, said window frame being provided with a central opening for positioning and securing said window plate within said opening, said window frame being covered with -a metallized surface coating substantially over the entire surface thereof to `.facilitate seal-ing of said ceramic window frame to `said w-aveguide section as well as to providing an electrical surface conductivity for the entire surface of said ceramic window frame, glass sealing means for sealing said ceramic window plate to said ceramic window frame `along the peripheral edge of said window plate without yany other part of `said ceramic window plate being covered with a .meta-llized surface coating, said ceramic window plate being separated from said waveguide section by Isaid Window frame, `rst solder means for sealing said Window frame to said waveguide section, and second means for sealing said ceramic window plate to said -ceramic window Iframe, said second meansbeing a high softening point glass.

References Cited by the Examiner UNITED STATES PATENTS HERMAN KARL SAALBACH, Primary Examiner. 

1. A HERMETICALLY SEALED CERAMIC WINDOW ASSEMBLY FOR USE IN WAVEGUIDE STRUCTURES COMPRISING A CERAMIC WINDOW PLATE; A CERAMIC WINDOW FRAME; A PAIR OF METALLIC SUPPORT MEMBERS: A PAIR OF REINFORCING FRAMES: SAID WINDOW FROM HAVING A CENTRAL OPENING FOR POSITIONING AND SECURING SAID CERAMIC WINDOW PLATE; SAID WINDOW FRAME HAVING A METALLIZED SURFACE COATING OVER ITS ENTRE SURFACE ADAPTED TO FACILITATE SEALING OF THE WINDOW FRAME TO THE CERAMIC WINDOW PLATE AND SAID PAIR OF METALLIC SUPPORT MEMBERS, SAID CERAMIC WINDOW PLATE HAVING A METALLIZED SURFACE COATING ONLY ALONG ITS PRIPHERAL EDGE TO FACILITATE SEALING OF THE WINDOW PLATE TO THE CERAMIC WINDOW FRAME, SAID CERAMIC WINDOW PLATE BEING SEPARATED FROM SAID WAVEGUIDE ASSEMBLY BY SAID WINDOW FRAME EACH OF SAID SUPPORT MEMBERS HAVING A FIRST ARM SEALED TO SAID CERAMIC WINDOW FRAME AND A SECOND ARM SEALED TO SAID REINFORCING FRAME AND THE WAVEGUIDE STRUCTURE; FIRST MEANS FOR SEALING SAID CERAMIC WINDOW PLATE TO CE RAMIC WINDOW FRAME; SECOND MEANS FOR SEALING SAID FIRST ARM TO SAID CERAMIC WINDOW FRAME; THIRD MEANS FOR SEALING SAID SECOND ARM TO SAID REINFORCING FRAME AND SAID WAVEGUIDE ASSEMBLY; AND FOURTH MEANS FOR SEALING SAID REINFORCING FRAME TO SAID WAVEGUIDE ASSEMBLY; SAID FIRST THROUGH FOURTH MEANS FOR SEALING BEING SOLDER; THE THICKNESS OF SAID SUPPORT MEMBER BEING CONTROLLED TO SUBSTANTIALLY ELIMINATE THERMAL STRESS FROM SAID CERAMIC WINDOW PLATE; SAID REINFORCING FRAME FASTENING SAID CERAMIC WINDOW FRAME THROUGH SAID SUPPORT MEMBER TO PROTECT SAID CERAMIC WINDOW PLATE AND SAID CERAMIC WINDOW FRAME FROM EXTERNAL FORCES. 